baffle: Used to mount a loudspeaker, this is usually a board or other plane surface inside the speaker cabinet.

balance: The difference in the amount of signal provided to the left and right stereo channels that changes the volume of each speaker individually.

bass frequency: The low end of the audio spectrum--between approximately 20 Hz and 400 Hz.

bass trap: An acoustic treatment applied to rooms that can absorb excess bass, often used in expensive home theatre rooms.

bipole: Speaker drivers that face both the front and rear of the speaker cabinet causing sound to project in both directions. Also see dipole.

C

centre channel speaker: The speaker mounted in front of the listener(s) and designed specifically for midrange frequencies such as for movie dialogue and certain special effects

channel: The guided path an audio signal travels through a circuit during playback. Surround sound consists of multiple individual channels such as the left front, right front, centre, and rear
channels working together.

coaxial: For speakers, it refers to a speaker with one driver in the middle of, and on the same axis as, another driver. Otherwise it refers to an audio or video cable with a single centre pin that
acts as the hot lead and an outer shield that acts as a ground.

codec: Data algorithms that determine the compression method and rate for a piece of digital audio, such as MP3, AAC, etc., and then decode it, allowing playback.

controller: In home audio terms, this is a broad term that describes a receiver that's combined with a preamp and/or a surround sound processor.

contour: See loudness control.

crossover: The part of a speaker that determines which frequencies go to which speaker, such as sending low frequencies to a subwoofer, for example.

crossover frequency: The "cutoff" frequency that causes a crossover to divide an audio signal between the subwoofers and other speakers. The most common crossover frequency is 80
Hz.

D

damping: The control of vibration by electrical or mechanical means, often used to control or eliminate ambience.

damping material: Material that absorbs sound waves and reduces acoustic reverberation or echoing by converting the sound waves into a different form.

decibel (dB): A unit of loudness usually ranked between 0 dB (the threshold of human hearing) and 140 dB (the point where loudness can cause pain or hearing damage).

delay: The time difference between audio leaving the speaker and its perception at the ear. Dipole speakers introduce a deliberate delay in order to control the size of the
soundstage.

diaphragm: The part of a speaker attached to the voice coil that moves back and forth to produce sound, usually in the shape of a dome or cone.

diffusion: In terms of audio, the scattering of sound waves that makes it difficult to tell which direction the sound is coming from.

digital audio server: Basically a hard drive attached to a network, a digital audio server stores audio files such as MP3 or WMA and allows playback on various devices, often across a wired
or wireless home network.

dipole: Similar to bipole speakers in that there are drivers facing in opposite directions, but dipole speakers are wired electrically "out of phase," meaning there is a delay between sound leaving
the front and rear speakers. Often used to introduce diffusion for a more ambient home theatre effect.

dispersion: The spreading of sound over a wide area.

distortion: Any corruption of an audio signal between the input and output. Usually manifests as static or as a harsh scratching sound--such as when bass is turned up louder than the speaker
can handle.

Dolby Digital: An encoding system that digitally compresses up to 5.1 discrete channels of surround sound audio (left front, right front, left surround, right surround, centre, and bass) into a
single bitstream that can be recorded onto digital media such as DVD, Blu-ray, etc. A Dolby Digital processor needs to be present in order to decode this signal back into the original surround sound
channels.

Dolby EX: Often called 6.1 surround sound, Dolby EX enhances Dolby Digital by adding a surround rear channel to 5.1 soundtracks. EX works on Dolby Digital systems, but an EX
processor must be present to decode and add the sixth channel.

driver: Refers to either a speaker without an enclosure or to the active element of a speaker system that causes the diaphragm (speaker cone) to move.

DTS and DTS ES:Digital theatre Systems is a digital sound recording format developed for movie soundtracks that records 5.1 audio channels onto select CDs and DVDs. Requires a
player with DTS output connected to a DTS processor. DTS ES adds a sixth channel similar to Dolby EX.

dynamic range: The difference between the lowest and the highest levels in audio, expressed in decibels.

E

efficiency: A ratio or percentage describing the useful power output to the power input of a speaker. This is measured by the sound pressure level (SPL) produced by the speaker when one
watt of power is put through it, measured one metre away from the speaker.

enclosure: An acoustically designed housing or structure for a speaker.

equalisation: The attempt to reproduce a desired frequency response through the use of graphic equalisers or tone controls.

equaliser: A device that compensates for undesired frequency levels of a system or speaker.

excursion: The movement of the cone or diaphragm of a speaker. Higher volts or amps will increase excursion.

F

feedback: In electronics, the return of a portion of the output of a circuit back into its input. In audio, a harsh or squealing sound caused by the signal from the output of a sound system going
back into a microphone input.

filter: An electronic device that allows certain frequencies (low or bass frequencies, for example) to pass while preventing others.

frequency: The number of vibrations or oscillations in units per second, measured in hertz (Hz). Can describe both pitch, as in musical instruments, and repetitions of a signal per second, as in
electronics.

frequency response: The rate of effectiveness at which a device, such as a speaker or amplifier, accepts and then transmits incoming frequencies; measured as a range of hertz. E.g., 20-
16,000 Hz.

full range: In audio, the entire audible spectrum: 20 Hz - 20 kHz.

G

gain: An increase in the strength of a signal, expressed either as a ratio of output to input voltage and current or as power expressed in decibels.

ground: A cable connected to a piece of metal (often the chassis of the object being grounded) used to protect against electrical shock in an electronic device carrying a live
current.

ground loop: Unwanted hum originating from undesirable current within a ground conductor owing to extra current originating from a second source of voltage.

H

harmonic: A sound in a series of sounds whose frequencies are multiples of a base frequency.

HDMI:High Definition Multimedia Interface is a high-speed audio/video connection that allows the passing of uncompressed digital signals in a single cable. It is now the standard AV
connection type between AV receivers, HDTVs, and movie players such as DVD and Blu-ray.

headroom: The difference between the average operating power level of an amplifier and the point at which clipping or distortion happens.

hertz (Hz): A unit of measurement; the cycles per second used to indicate the frequency of sound or electrical waves.

high pass: All signals above a given crossover frequency. If a crossover frequency is set at 16,000 Hz, for example, the high pass is everything above 16,000 Hz.

horn: A flared structure, usually either round or four sided, used to assist a loudspeaker. Loudspeakers with horns are considerably more efficient than coil loudspeakers in turning electrical
into acoustic energy, meaning it takes less power to achieve greater volume and clarity.

I

imaging: A system's ability to create the illusion of sounds at specific locales in the room, ideally in the same spatial relationship the sounds existed in at the time of recording.

impedance: The opposition to an alternating current flow presented by a circuit, expressed in ohms. Used to rate input and output characteristics of components so that a proper "match" can
be made when connecting two or more electronic devices, such as a loudspeaker and amplifier.

inductor: A coil of wire used to create a low-reacting impedance, offering low resistance at low frequencies and high resistance at high frequencies. An inductor passes low frequencies and
attenuates or rolls off high frequencies.

infinite baffle: A loudspeaker design principle, which is to isolate the front and rear radiation from a loudspeaker. Sealed-box loudspeakers incorporate this principle.

J

jack: The point of connection on an electronic device into which a matching connector can be plugged.

jitter: The slight variation of an input signal that can induce errors and/or loss of information in the output signal.

K

kilohertz: A frequency of one thousand cycles per second (1 kHz).

L

limiter: An electronic circuit used to prevent the amplitude of a signal (volume, for example) from exceeding a specified level.

listening fatigue: A phenomenon resulting from prolonged listening to sound whose distortion content is too low to be audible but high enough to be perceived subliminally, causing discomfort
such as headaches.

localisation: In audio, the placement of phantom images in specific positions across the soundstage. Similar to imaging.

loudness control: A volume control with special circuitry added to compensate for the normal decreased hearing ability of the human ear at the extreme ends of the audio range when listening
to lower sound levels. A typical loudness control boosts the bass frequencies and, to a lesser extent, the high frequencies. Also called contour.

low-level detail: The amount of clarity in the subtlest parts of sound reproduction, such as reverberation decay, string vibration, aspirate syllables or breathing in vocals, etc.

low pass: All signals below a given crossover frequency. If a crossover frequency is set at 16,000 Hz, for example, the low pass is everything below 16,000 Hz.

M

midrange: Smaller than a woofer but with more surface area than a tweeter, this type of driver produces sound in the 300-5000 hertz range. It can also refer to the range of sound above bass and below treble, which includes most sounds produced vocally.

magnet: The voice coil reacts to a stationary field created by a permanent magnet to produce sound.

midbass: A driver that is designed to be used to produce both bass and midrange sounds, it can also refer to the middle of the bass section of the frequency range, somewhere between 50-100 hertz.

monaural: Also known as mono, it's the use of an amplifier in only one channel for input and output.

motor structure: The part or parts of a speaker that move the diaphragm and produce sound.

N

neodymium magnet: Stronger than conventional magnets, neodymium magnets are smaller and sometimes used in headphones and loudspeakers.

net volume: The amount of airspace inside the speaker enclosure, irrespective of any bracing, vents, or speaker components.

noise: Sounds not part of the original soundtrack that can be detected in a speaker's output, usually as undesirable hissing, buzzing, or crackling.

O

ohm: A unit of measurement that indicates how much something resists or impedes the flow of electricity.

omnidirectional: Sound that comes from all directions. As frequencies decrease, so does directionality; woofers and other low-frequency drivers tend to produce this effect.

on-axis: The state of being precisely lined up with the emitter of the speaker, headphones being one example, and sitting directly in front of a speaker another.

optical input: A type of speaker connection that uses optic fibres to transmit a signal as light rather than a current through copper or similar conductive substances.

output: An electrical signal that is sent from the amplifier to one or more speakers.

P

passive radiator: Similar to drivers but lacking any kind of active motor assembly, these devices react to pressure within the speaker enclosure and reinforce the output of lower frequencies.

peak power handling: An estimated amount of maximum power a speaker handles during a short but intense burst of sound.

pole piece: A component that focuses energy from the speaker magnet into a magnetic circuit.

polypropylene: A synthetic material used for their light weight, low resistance, and minimum resonance to make speaker cones.

port: An opening in an enclosure that allows sound to pass through.

Q

R

resonance: A vibration caused by the application of external energy--in this case the vibration of a speaker's cone. Excess vibration can interfere with a speaker's ability to reproduce sound accurately.

receiver: A device that receives signals from various input devices, interpreting and amplifying those signals before sending them to output devices.

resistor: An electrical circuit component that looks like a small cylinder with wires on either end. They can reduce the flow of electrons through the circuit to serve amplification or switching requirements.

resonant frequency: The frequency where the cone vibrates with the least amount of inertia.

room response: The interaction of a speaker system with a room or other enclosed environment, which can impact its effectiveness.

S

sensitivity: A measurement of a speaker's effectiveness in converting watts of power into decibels of sound.

slew rate: The ability of an audio device to faithfully reproduce fast changes in amplitude. A slow rate can soften the signal, distorting the sound.

sound projector: A bar-like enclosure with several--sometimes dozens--of drivers that produce a surround sound experience. By digitally focusing the sound and controlling the delay of each driver, the listener perceives the sound coming from different points in the environment.

soundbar: See sound projector.

soundstage: The sense of depth, width, and height to a audio reproduction. A speaker with rear and front speakers in high and low positions can create the audio "image" of actually being in the environment where the original music or track was recorded.

subwoofer: A speaker designed exclusively for low frequencies, consisting of one or more woofers in a sealed or ported enclosure.

surround sound: The concept of expanding an audio reproduction from one dimension (monaural or left/right channels) to a three-dimensional sound.

sweet spot: The optimal physical listening position in a sound field where all the outputs of a speaker system overlap and the overall "image" of the reproduced sound is most convincing.

T

three-way speakers: Also known as triaxial speakers, this type of enclosure has separate woofer, midrange, and tweeter drivers.

THX: Developed for cinema but is also available on certain AV receivers, THX is a standard of quality assurance concerned with providing a high-quality, predictable playback environment as close as possible to the intentions of the original mixing engineer. In a receiver, it denotes the presence of a special THX crossover circuit whose use is part of the THX standard.

timbre: The distinctive quality or substance of a sound as it is produced by a voice or instrument.

transducer: A device that converts one form of energy into another. In a speaker's case, electrical energy is converted to acoustic energy.

tube: A type of woofer enclosure with a woofer on one side and a port or passive radiator on the other.

unloading: A lack of spring or pressure on a woofer by its enclosure, which can lead to out-of-control vibrating.

V

virtual surround sound: Also known as VSS, it is an audio system that, using one or two speakers, can create the perception that there are more sources of sound than are actually present.

voice coil: A coil of wire attached to a cylinder, it creates a magnetic field that varies by the amplified signal sent to the loudspeaker. In concert with other components it converts electrical output from the amplifier into mechanical energy, which can then be heard as sound.

voice coil former: The component around which the voice coil is wound, usually made of heat-resistant materials.

voice coil gap: The space between the magnet and pole piece where the voice coil can move freely, which creates vibrations in the speaker cone.

volt: A unit of measurement that indicates how much electromotive "pressure" is required to move a current through a circuit.

W

watt: A measurement unit that indicates the rate of energy use or production.

woofer: A specialised speaker that reproduces bass and lower midrange sounds. They are typically made of stiff but lightweight materials. They may be included in a two- or three-way loudspeaker or in their own enclosure in a subwoofer.